1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to an improvement for preventing displacement between an electrode buffer plate and other members.
2. Description of Background Art
In a semiconductor device of a flat-pack type which is mainly used for large power circuits, members such as electrode buffer plates, electrode conductor, etc. are laid on a semiconductor substrate, and the structure thus Obtained structure is contained in an insulating cylinder. The electric buffer plates are provided in order to buffer or compensate stress in the semiconductor chip which may be caused due to difference between respective coefficients of thermal expansion of the semiconductor chip and the electrode conductors.
FIG. 9A is a side view showing an appearance of a conventional semiconductor device and FIG. 9B shows an enlarged sectional view of FIG. 9A by shortening the section Q thereof to show the internal structure. In FIG. 9B, the semiconductor element I is a gate turn-off thyristor in which a cathode conductive film 4 and a gate conductive film 5 are formed in mutually separate state on the bottom major surface of a disk-shaped semiconductor substrate 3, .RTM.nd the semiconductor substrate 3 is fixed by soldering to a conductive reinforcing plate 2 which acts also as an anode electrode. In the drawings, the thicknesses of these conductive films 4 and 5 are exaggerated for convenience of illustration. At the circumferential end of the semiconductor substrate 3, an insulating protective layer 6 is formed.
This semiconductor element I is inserted in an insulating guide ring 9 and the position of the element 1 in the horizontal direction in FIG. 9B is restricted by the guide ring 9. The guide ring 9 is internally fitted to the insulating cylinder 10. On the top surface of the reinforcing plate 2, there are placed an anode buffer plate 7 and the anode conductor 8 in this order. The position of the anode buffer plate 7 in the horizontal direction is restricted by the projection 9a of the guide ring 9. To the anode conductor 8, there is fixed an anode flange 11. The other flange 12 which is fixed to the end part of the insulating cylinder 10 and the anode flange 11 are arc-welded at the edge 13.
Underneath the semiconductor element there is a cathode/gate assembly CG whose outer shape is shown by broken lines. This cathode/gate assembly CG includes a cathode buffer plate and a cathode conductor, and has members which constitute an electrical channel from the gate conductive film 5 to a gate terminal 30. Also, the cathode/gate assembly CG is connected by a cathode flange 14 to the insulating cylinder 10. When a control signal is supplied to the gate terminal 30, the electrical channel between the bottom surface of the cathode/gate assembly CG and the anode conductor 8 is opened or closed by the switching action of the semiconductor substrate 2.
The semiconductor device of FIG. 9B is assembled on the premise of being used under the condition where certain pressure represented by an arrow F--F is applied to the anode conductor 8 and the cathode/gate assembly CG. In other words, by such pressure, uniform electrical contacts between respective members are maintained, and thereby normal operation of the semiconductor device is attained.
However, before assembling this semiconductor device into an electric equipment, no such pressure is applied. Accordingly, in case of transporting such semiconductor device before assembling the same into an electric equipment, it may occur for the anode conductor 8 to float up by vibration in the transportation and the like. This is because the anode flange 11 is formed of a soft metal such as copper and is often deformed by vibration and the like.
When the floating occurs, a gap is formed between the anode conductor 8 and the reinforcing plate 2, and the anode buffer plate 7 is displaced to pass over the projection 9a of the guide ring 9, as shown by the arrow K. If such displacement occurs, it becomes no longer possible to maintain uniform contact between respective members. As a result, current distribution in the semiconductor substrate 3 in operation becomes non-uniform to cause abnormal generation of heat or breakdown of the substrate 3.
In order to prevent such a problem, there may be an improvement to make the height H of the projection 9a higher. However, as the gap in the vertical direction between the guide ring 9 and the anode flange 11 is relatively narrow, it is difficult to take the height H of the projection 9a sufficiently high.